harmonic analysis with specified fundamental

[tca-adam]

HI all,

I am a bit lost with the multitude of harmonic analysis VIs there are in the LV8 palette and am having difficulty finding the one I need.

I have a waveform I want to apply harmonic analysis to. It had a fundamental frequency of 150Hz and the I want to see if there any component present at 50Hz.

Running it through the standard Harmonic Analysis VI successfully finds the 150Hz fundamental and the harmonics greater than that, but I can't work out how to display the amplitude of the 50Hz component.

I need to report fundamentals in amplitudes.

thanks

[gwd]

The harmonics of 150 Hz are n*150 Hz where n is an integer. What you are after is a subharmonic, and (at least in 7.1) the harmonic analysis vi will not find it.

You might be able to use an fft vi, or you might have to write something yourself.

Consulting a signals textbook might be a good idea.

[DavidJCrawford]

I have attached my take on how you might do it. This example in LV8 uses the Express Spectrum Measurement, Express Extract Portion of Signal and Get Y Value to get the peak amplitude in dB at your fundamental frequency and the specific frequency of 50Hz.

Hope this helps

David